1. Field of the Invention
The present invention is directed to a precision drill sharpener and a grinding wheel assembly adapted to be used with the precision twist drill sharpener.
2. Description of Related Art
There are a number of drill sharpener machines available today, some of which can sharpen common twist drills to a like-new drill geometry. However, many of those machines require rather skilled operators, and others only approach standardized drill geometry.
U.S. patents directed to drill sharpener machines and attachments, such as twist drill chucks, include: U.S. Pat. Nos. 4,916,866, Bernard et al; 4,485,596, Bernard et al.; 4,471,481, Bernard et al; and 4,001,975, Bernard et al. The recently issued Christian et al. patent, U.S. Pat. No. 5,400,546, presents a design that all but eliminates the need for skilled operators, and substantially removes all of the guess work from sharpening the drills. Historically, common twist drills have been a very standardized tool. The geometry at the cutting end was a standardized geometry, generally selected by the Metal Cutting Tool Institute as the best geometry for all general purpose drilling, and had an included point of 118xc2x0, a lip relief of 6xc2x0 to 18xc2x0 (depending on drill diameter), and a chisel edge accurate to within 0.004 inch with the axis of the drill. In recent years, many new drill point geometries have become commonly used for special and general purpose drilling. The most prominent variations on the standard 118xc2x0 point are the 118xc2x0 xe2x80x9cSxe2x80x9d or Spiral point, the 135xc2x0 split point, or a combination of the two. In addition, a higher degree of chisel edge accuracy, down to 0.002 inch, is becoming more common. These new points are being used more and more because of their superior cutting ability, self-centering characteristics and ability to produce more accurate holes. Currently, about 30% to 40% of all twist drills produced in the United States are made with one of these point variations. Drills with the traditional standard point geometry, or the other mentioned variations, are purchasable at hardware stores and industrial supply distributors by homeowners, hobbyists, auto mechanics, building tradesmen, millwrights and machinists.
Good-quality, high-speed, steel twist drills are expensive; for example, the average current list price for xe2x85x9-inch size, with a traditional 118xc2x0 point, is about $0.60; for {fraction (5/16)}-inch size, about $1.75; and for xc2xd-inch size, about $4.00. Prices for drills with xe2x80x9cspecialxe2x80x9d drill points are usually double in cost. Even with the twist drills being so expensive, only a very small percentage of the twist drills purchased are ever resharpened, because it has been very difficult for even a master machinist to resharpen the cutting tips by hand and produce the most efficient or desired geometry. Generally, drills resharpened by hand remove material inefficiently, quickly become overheated, lose their sharpness and are soon scrapped.
For these reasons, thousands of persons using twist drills scrap a number of twist drills per day at an estimated average cost of $2.00 per each drill. Such loss can amount to a hundred or more dollars per week per manufacturer.
The size of possibly not less than 95 percent of all twist drills manufactured and used is within the range of {fraction (1/16)} inch and xc2xe inch in diameter, and within this range, there are many fractional-inch sizes, letter sizes, numeral sizes and millimeter sizes. One of the main objects of this invention is to provide a drill sharpener whereby all of these different sizes of drills, about 300 in all, can be handled by one super precision drill sharpener mechanism.
It is also a primary object of this invention to provide a precision drill sharpener that attains the goals accomplished by the sharpener design in the aforementioned Christian et al. patent, e.g., eliminating guess work and the need for skilled operators in order to obtain precision sharpening, while providing various enhancements, such as a highly compact design, a new grinding wheel assembly configuration, and a machine that is substantially highly economical to manufacture, such that it can be affordable to hobbyists, home craftsmen, auto mechanic shops and building tradesmen.
It is an additional important object of the present invention to provide a simple lever and spring clip subassembly as a means for properly aligning or timing a drill in the drill chuck.
It is an additional important object of the present invention to provide an adjustment mechanism for changing the angle at which the drill point will be sharpened, and a corresponding adjustment mechanism for properly aligning the drill in the chuck for the proper drill point angle.
It is a further important object of the present invention to provide a drill chuck that is open at its back end to allow for manual manipulation of the drill while the drill and chuck are disposed in the alignment port, in order to effect the proper alignment or timing of the drill.
It is a further object of the present invention to provide a drill sharpener using a small diameter grinding wheel operated at high speed to provide cutting rates comparable to large industrial sharpeners, but that will not overheat and thus be rendered ineffective by such overheating.
It is a further object of the present invention to provide a grinding wheel construction that will electrically insulate a steel grinding wheel from the motor shaft to which it is fastened in a direct drive system.
It is yet an additional object of the present invention to provide a drill sharpening device having a point-sharpening port and a point-splitting port each oriented such that the same grinding surface on the grinding wheel is used to both sharpen and split the point.
The above and other objects of the invention are accomplished by providing a drill sharpener that is compact in design, using a high-speed, small diameter diamond-plated grinding wheel to quickly and efficiently sharpen the drills. The sharpener has a simple drill alignment system employing a button or lever-operated pair of alignment clips and a chuck that is open and accessible from the back end of the chuck. The port containing the drill alignment clips is disposed in the same housing as is the grinding wheel and its associated ports.
The alignment port, the drill chuck, and the primary sharpening port are all designed such that the alignment port may be rotated or reoriented to properly align drills having different drill point geometries, and the primary sharpening port is similarly adjustable to present the drill point to the grinding wheel at the desired angle. The primary sharpening port and the point-splitting port are arranged at diametrically opposed positions on either side of the grinding wheel of the drill sharpener, and each of these ports is designed to receive the chuck to present the drill point to the same grinding wheel surface at appropriate orientations such that the same grinding surface is used to sharpen the drill point, and, where desired, to split the drill point, or resharpen the split point surfaces.
The grinding wheel has several important design features that have been developed and incorporated so that the sharpener can meet the requirements for UL (Underwriters"" Laboratories) listing approval. The body or substrate of the grinding wheel would normally be solid steel, an electrically conductive metal. The motor shaft, also made of steel, is required to be electrically insulated from the grinding wheel in order to obtain UL approval. The grinding wheel is thus made up of central hub made of a high-temperature plastic material, and having a diamond-plated steel grinding ring disposed at an upper peripheral position, with the grinding ring member secured to the plastic hub by a circular cast aluminum heat sink disk. The plastic hub has a central bore and is press fitted onto the steel motor shaft, thus electrically isolating the shaft from the steel grinding ring member.
The high speed at which the motor operates, and the use of a small diameter grinding ring, result in a potential to generate enough heat to melt even high-temperature-rated plastics, so the finned aluminum heat sink disk serves the dual purpose of retaining the grinding ring in position and carrying away the excessive heat generated in the grinding operation.